This invention relates to high resolution television or other information display wherein the horizontal scan lines of the camera (or equivalent signal source) are vertically deflected to increase the video information transmitted and the horizontal scan lines of the television receiver or monitor are vertically deflected in synchronism with the source, and more particularly to apparatus for controlling the phase and amplitude of the vertical deflection of the horizontal scan at the CRT of a television receiver or monitor.
In a television picture, there are two independent resolution factors, namely horizontal resolution, which depends largely upon system bandwidth, and vertical resolution, which depends largely upon the number of active scanning lines in a frame. Various techniques have been employed to increase horizontal resolution. For example, although the video bandwidth is limited to about 4 MHz, the video signal may be processed by a studio with twice the bandwidth of the transmitter on the theory that the better the picture into the transmitter, the better the picture at the receiver. But vertical resolution has, in the past, remained limited by the number of active scanning lines.
In the United States, the National Television Systems Committee (NTSC) has prescribed as a standard the total number of scanning lines of 525 divided into two interlaced fields. This number is significantly reduced to about 485 active scanning lines by the necessary vertical blanking time (approximately 7.5 percent of the total time for scanning 525 lines). Other factors may further degrade horizontal resolution, such as scanning spot size. It would be possible to increase vertical resolution by doubling the number of active scanning lines and decreasing the spot size, but that would reduce the horizontal resolution for a given bandwidth and frame rate. The problem is to increase vertical resolution without deviating from the NTSC standard of 525 lines. The problem exists as to other standards adopted in other parts of the world, such as PAL and SECAM, since any finite number of prescribed lines less than 1000 may significantly limit the vertical resolution to substantially less than the horizontal resolution.
In a patent application Ser. No. 515,220 now U.S. Pat. No. 4,589,012 filed by Jimmie D. Songer, and assigned to the assignee of this application, vertical resolution is increased for standard television by modulating the vertical scan axis (deflection) of a television camera at a multiple of the color carrier, for example, twice the color carrier frequency of 3.579545 MHz, such that each active scanning line traverses an undulatory path rather than a straight line, i.e., oscillates about the normal scan line. The amplitude of the modulation is preferably sufficient for interlaced lines of a frame to intrude the area of adjacent lines of interlaced fields, which is modulation with an amplitude equal to at least plus and minus one half line spacing of each field above and below the center of the spot on the normal scan line. The video signal thus produced by actually scanning areas above and below the normal scan lines is then transmitted just as for the normal scanning lines, which can be within the vestigial bandwidth limit of about 4.2 MHz for NTSC broadcast transmission, without loss of the high resolution information in the signal transmitted, using a system disclosed in a copending application Ser. No. 654,381 by Arthur C. Phelps filed Sept. 25, 1984, and assigned to the assignee of this application.
In accordance with the system of the Phelps copending application, virtually all of the potential increase in vertical resolution of the aforesaid high resolution television system is preserved in the composite video (Y, I, Q) transmitted within the narrow color subcarrier sidebands of about 3.6 MHz by synchronously detecting high resolution television (HRT) information in the luminance (Y) signal at the vertical scan modulation frequency, and modulating the HRT information with a signal at some predetermined fraction of the vertical scan modulation frequency that is well within the narrow vestigial bandwidth, of the broadcast signal such as one sixth (1.1931816 MHz) the modulation frequency of twice the color carrier frequency of 3.57945 MHz. The high resolution information on the Y signal is thus synchronously detected and then modulated at a lower frequency (.perspectiveto.1.2 MHz) that is above the color carrier frequency band of the Q signal which is 0.5 MHz and in phase with the Q signal so as to be distinct from the I signal in phase and distinct from the Q signal in frequency. The Y signal modulated with the HRT information (the vertically modulated scan information present in the composite video signal to be transmitted) is bandpass filtered to assure that the vestigial sideband of the video is within 4.2 MHz. That filtering removes the HRT information on the Y signal, but this same HRT information on the lower carrier frequency of 1.2 MHz can be transmitted along with the bandpass limited I and Q signals.
At the receiver, the color demodulator is not affected by the HRT information modulated at the same bandwidth (.perspectiveto.1.2 MHz) as the I signal but in phase with the Q signal. The I and Q signals, and the high resolution information modulated at 1.2 MHz, are separated by a bandpass filter and applied to a balanced demodulator using a 3.58 MHz reference frequency synchronized with the color carrier. At the input of the demodulator, the composite signal is bandpass limited so that the Q and I signals are applied to the demodulator separately for demodulating and then converting through a matrix of red, blue and green signals (R, G, B). The high resolution information at the output of the I bandpass amplifier is then synchronously detected using the same frequency and phase as used for modulating the high resolution information signal at 1.2 MHz at the transmitter. The high resolution information signal thus detected at the receiver is then modulated at the same frequency and phase as used in modulating the vertical scan at the television camera, and added to the Y signal for display with vertical modulation of the horizontal scan of the CRT display synchronized at the same frequency as at the source, using the color carrier as a reference to derive the modulation frequency, and controlling the phase and amplitude of modulation to be virtually the same as at the source. In that manner, the high resolution information of the composite video signal produced by the camera at the high vertical scan frequency, but transmitted at the lower frequency of 1.2 MHz in the Q channel, is displayed at the receiver.
The success of the high resolution television system just described depends upon control of the phase and amplitude of the CRT modulation. Consequently, an object of this invention is to provide a circuit for doubling the color subcarrier frequency at both the camera, or equivalent source, and the cathode ray tube (CRT) or equivalent display with independent phase and amplitude control.